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Ultrasound-guided interventional radiology in critical care

Savvas Nicolaou, MD, FRCPC; Aaron Talsky, BA, JD; Khalid Khashoggi, MD; Vicnays Venu, BSc

U ltrasound is a powerful, inex-pensive, and ubiquitous toolparticularly well suited forthe diagnosis and treatment

of critically ill patients. These patients areoften complex and may present with avariety of conditions and complications.For example, infections in this settingpose unique clinical challenges and areassociated with high mortality and mor-bidity. The mortality rate of patients ad-mitted to an intensive care unit (ICU)with an intraabdominal infection is ap-proximately 30% and significantly higherfor patients with recurrent or postopera-tive peritonitis (1). Rapid localization ofan infective focus is essential. Challengesare not limited to diagnosis. Operativemanagement strategies may be impracti-cal or impossible in light of the marginalclinical status of these critically ill pa-tients. Similar analysis can be applied to awide variety of clinical entities in thecritical care setting. Clearly, in this set-ting, increased application of bedside,minimally invasive, diagnostic, and inter-ventional techniques is highly desirable.

The desire to quickly and effectivelytriage, diagnose, and treat has fueled theuse of ultrasound as a screening tool inthe emergent and critical care settings.As technology has advanced, this modal-ity has become increasingly available andportable. Ultrasound machines may nowbe easily transported to the bedside, mak-ing it a convenient and effective tool forcritical care. Studies have reported appli-cation to a wide spectrum of emergentclinical presentations, including internalhemorrhage attributed to blunt abdomi-nal trauma, cardiac tamponade, ectopicpregnancy, renal colic (although the useof ultrasound in suspected renal colicmay be of limited value, especially wherecomputed tomography [CT] is readilyavailable), cholelithiasis, abdominal aor-tic aneurysm, and foreign body localiza-tion and removal (2, 3).

Few would disagree that it is inher-ently safer and more effective to performinterventions with direct visualizationrather than without. Not only can ultra-sound offer real-time imaging of the nee-dle tip during interventional procedures(Fig. 1) and multiplanar imaging, it canalso be performed at the bedside. Centersin Europe and Japan have pioneered theuse of ultrasound-guided procedures, andin these areas, ultrasound is now consid-ered the imaging modality of choice forguiding many diagnostic and interven-tional percutaneous procedures (4). Ini-tial applications included biopsies andfluid aspirations, but ultrasound is also

useful in guidance of thoracentesis, para-centesis, percutaneous nephrostomy, andcholecystostomy, localization of joint ef-fusions, and insertion of central catheters(3). Interventional ultrasound is gener-ally considered to be safe and effective,and we believe it is significantly under-utilized in critical care today. In the fu-ture, the frequency of various interven-tional procedures performed with the aidof this imaging modality will almost cer-tainly increase (5).

GENERAL PRINCIPLES

Indications. The indications for aspi-ration and percutaneous drainage of fluidcollections have been identified by theSociety of Cardiovascular and Interven-tional Radiology Standards of PracticeCommittee as: “the presence of an abnor-mal fluid collection with suspicion thatthe fluid is infected, the need for fluidcharacterization, or suspicion that thecollection is producing clinically relevantsymptoms” (6).

The main indications for percutane-ous drainage are to facilitate a cure andthus avoid the risks and morbidity asso-ciated with general anesthesia and sur-gery. It can also be utilized as a tempo-rary procedure that either delays thedefinitive operation until the patient isclinically stable or converts a multistageprocedure into a single-stage surgicalprocedure, the benefits of which are ob-vious in high-risk septic patients, partic-ularly in the critical care setting.

From the Department of Radiology, VancouverGeneral Hospital, University of British Columbia, Van-couver, British Columbia, Canada.

Dr. Nicolaou has not disclosed any potential con-flicts of interest.

For information regarding this article, E-mail:[email protected].

Copyright © 2007 by the Society of Critical CareMedicine and Lippincott Williams & Wilkins

DOI: 10.1097/01.CCM.0000260630.68855.DF

Ultrasound-guided intervention is becoming an increasinglypopular and valuable tool in the critical care setting. In general,image-guided procedures can expedite wait times and increasethe accuracy, safety, and efficacy of many procedures commonlyperformed within intensive care units. In the intensive care unitsetting, ultrasound has particular advantages over other imagingmodalities such as computed tomography and fluoroscopy, in-cluding real-time visualization, portability permitting bedside pro-cedures, and reduced exposure to nephrotoxic contrast agents.We review the technical and procedural aspects of a number ofultrasound-guided interventions appropriate for critical care pa-

tients. These include central venous catheter deployment, thoracen-tesis, paracentesis, and drainage of a wide variety of abscesses, andpercutaneous nephrostomy, percutaneous cholecystectomy, and in-ferior vena cava filter placement. Although we believe ultrasound issignificantly underutilized in critical care today, we anticipate thatwith the improvement of ultrasound technology and the innovation ofnew ultrasound-guided procedures, the role of ultrasound in theintensive care unit will continue to expand, with bedside ultrasound-guided interventions increasingly becoming the norm. (Crit Care Med2007; 35[Suppl.]:S186–S197)

KEY WORDS: ultrasonography; intervention; critical care

S186 Crit Care Med 2007 Vol. 35, No. 5 (Suppl.)

Contraindications. The only absolutecontraindication to percutaneous drain-age is if the path of the drainage catheterwould have to traverse a vital organ, suchas the heart or a major vessel, to drain thecollection.

All other contraindications are usuallyrelative and include a significant correct-able coagulopathy or the presence of ma-terial that cannot be effectively drainedthrough a percutaneously inserted drain-age tube, such as significant necrotic de-bris or a nonliquefied hematoma (Fig. 2).

TECHNIQUE

Informed Consent. Informed consentshould be obtained from all patients be-fore any procedure when possible. The

nature of the procedure should be ex-plained in a coherent fashion to eitherthe patient or the immediate family,making sure to outline all the associatedrisks and benefits.

Sedation and Antibiotics. A superficialabscess can often be drained utilizing lo-cal anesthesia only. Deeper pelvic andretroperitoneal abscesses are better man-aged with the aid of conscious sedationand the assistance of anesthesia. An in-travenous narcotic in combination with ahypnotic sedative is usually appropriate.In this scenario, physiologic monitoringof the patient’s vital signs is a must. Inour institution, broad-spectrum antibi-otic coverage is administered before theprocedure to protect against life-threat-ening bacteremia.

Localization. We advocate utilizingimaging before intervention to localizethe fluid collection, assess its size, char-acterize the fluid composition, and toplan a safe route for percutaneous drain-age. Selecting ultrasound vs. CT is gen-erally a reflection of operator preferenceand expertise. However, no single imag-ing modality used to guide percutaneousdrainage is appropriate for all abdominalfluid collections or abscesses. It is impor-tant to realize that each case is unique andthat the method and approach employed toreach a potentially infected fluid collectionshould be tailored to the patient, the pro-cedure, any specific circumstances, and theexpertise of the operator. We propose thatultrasound-guided intervention is particu-larly useful in the ICU setting given that itis portable, allows imaging in numerousplanes, and allows real-time visualization ofthe needle and catheter, which in turn en-ables the operator to directly visualize andavoid vital structures. In addition, color-Doppler flow can also be employed to ac-curately identify vessels, allowing for supe-rior planning of approach in drainingabscesses.

Drainage Technique and Catheter Se-lection. Once an entry site has been se-lected, the skin is sterilized and draped. Alocal anesthetic agent is used to initiallyanesthetize the skin, and a small skinincision is made with a surgical blade.Small Kelly forceps can also be utilized toexpand the skin incision and separatesome of the subcutaneous tissues, allow-ing for a larger access site for the initialdrainage needle. No clear scientific evi-dence exists to define whether a particu-lar catheter design or size is superior forthe evacuation of infected fluid collec-tions. Catheters are available with andwithout parallel sump channels in bothlocking and nonlocking tip designs.Locking tip designs tend to provide excel-lent purchase within the infected fluidcavity. Catheter sizes can range from 6 to30 Fr. Regardless of selected cathetersize, the basic principle remains that thecatheter should be large enough to drainthe fluid into which it has been inserted.For example, 6- to 8-Fr catheters can beplaced into the gallbladder for a percuta-neous cholecystostomy, 8-Fr cathetersare placed percutaneously to drain pleu-ral fluid, most abdominal abscesses aredrained via a 12- to 16-Fr catheter, andcomplex infected fluid collections canusually be drained with 19-Fr catheters.

Fluid can frequently be completelyevacuated at the time of the initial drain-

Figure 1. Left, ultrasound image of an intraabdominal fluid collection that demonstrates a linearechogenic (arrows point to bright linear region) structure representing a needle traversing thesubcutaneous tissue anteriorly, with the needle tip present centrally (arrowhead points to needle tip),within the fluid collection. Right, characteristic appearance of a drainage catheter in an ultrasoundimage; arrows point to parallel tubular echogenic densities representing the catheter.

Figure 2. Left, curvilinear probe ultrasound image of the subcutaneous tissues anterior to the femurreveals a heterogeneous, solid, infected collection between the callipers (arrow points to phlegmon) inthe appropriate clinical setting. This would not be amenable to percutaneous drainage because thecollection is not liquefied (i.e., it is not cystic). Right, high-frequency linear transducer ultrasoundimage of the previously identified collection a few days later now identifies the collection to be liquefied(arrow points to cystic liquefied collection), which now would be amenable to percutaneous drainage.Color-Doppler flow is also helpful in planning therapeutic interventions because it can identify thevasculature (arrowhead). Thus, the percutaneous approach to this collection should be from anoblique anterior location on the left.

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age and may become blood tinged as thecavity collapses. Some interventional ra-diologists advocate irrigation of the cavityat the time of drainage with sterile saline(or metronidazole for hepatic abscesses).However, it is commonly accepted thatirrigation of the cavity under pressureshould never be performed, as this canseed bacteria into the blood stream andproduce serious septic consequences (7).

Catheter Placement: Trocar Tech-nique. With trocar technique, an initial19-gauge fine needle is used to aspiratethe fluid and as a tandem localizer. Acatheter is then fit over a metal stiffeningcannula, and a sharp metallic trocarstylet is placed within the cannula topuncture the cavity and for insertion. Theentire assembly is then advanced into thefluid collection. The catheter is then ad-vanced from the cannula, and a distalloop is formed and tightened to ade-quately secure the catheter within thefluid collection. This method usuallyworks best for large and superficial fluidcollections.

Seldinger Technique. This techniqueinvolves a guidewire exchange method. Aguidewire is advanced through the aspi-ration needle and coiled within the fluidcollection. The needle is then removedfrom over the guidewire leaving it inplace as an anchor for the passage ofnumerous dilators aimed at widening thetrack to accept the chosen size of drainagecatheter. The catheter/cannula assembly isthen placed over the guidewire into thefluid collection. The guidewire and innercannula are removed while the drainagecatheter is simultaneously advanced. Thedistal locking tip of the catheter is reformedto prevent dislodgement. On ultrasound,the needle tip and catheter appear as lineartubular echogenic (bright) regions withinthe fluid collection (Fig. 3).

Postprocedure Care and Follow-up. Ifa sump tube has been inserted, the cath-eter is usually attached to a low-pressure,continuous wall suction apparatus. If aCope loop catheter has been inserted(nonsump), it is usually connected to aJackson-Pratt continuous suction bulb.The patient should be monitored in theICU and the catheter flushed with 3–5 mLof sterile saline to maintain patency ofthe catheter (7).

Assessment of Results. After drainageof an abscess, three clinical scenariosmay exist.

1. Minimal drainage of �10 mL/24 hrswith clinical improvement. This is the

anticipated result after successfuldrainage of an abscess. A sinogram canbe performed before catheter removalto delineate a residual cavity.

2. Minimal drainage of �20 mL/24 hrswithout clinical improvement repre-sents the most adverse situation. Thisgenerally identifies that the underly-

ing problem has not been addressed.Repeat imaging to search for addi-tional fluid collections is warranted.The catheter track must also be in-spected for potential complications. Ifno additional injuries or fluid collec-tions are identified and the initial fluidcollection has been evacuated, investi-

Figure 3. Top, catheter assembly unit: 1) locking-tip catheters of different sizes, 2) trocar stylet, and3) cannula stiffener. Middle, trocar technique. This usually involves the placement of a catheter intoa collection without guidewire assistance. Within the center of the catheter, a sharp stylette, whichkeeps the catheter straight and has, as its tip, a sharp, cutting-edge metal needle, is used to perforatethe collection. Initially, a 20-gauge needle (N) is inserted into the collection under ultrasoundguidance (a). Under real-time ultrasound guidance, the largest possible catheter (C) with a sharpstylette is trocared along the side of the needle into the collection (b). A pop is usually felt when thetip is in the cavity, followed by aspiration of fluid to confirm catheter placement. The stylette andsharp, cutting-edge needle are then removed from the catheter while simultaneously advancing thecatheter (T) into the collection (c). Bottom, Seldinger technique–guidewire exchange technique. Thisis a multistage technique that also initially utilizes a 20-gauge needle that is inserted into thecollection under ultrasound guidance. A guidewire is then introduced through the needle into thecollection. Dilators are then introduced over the guidewire, dilating up the tract to the appropriate sizethat will accommodate the largest possible catheter. The final stage of the technique, as identified inthe diagram, involves the pigtail catheter being introduced over the guidewire while simultaneouslyremoving the cannula from within the catheter and still maintaining purchase with the cavity, makingsure the guidewire is not accidentally removed from the collection until the pigtail catheter is securelypurchased within the collection. Once the pigtail catheter is secured within the collection, theguidewire is then removed.


gation for alternate causes is recom-mended.

3. Continuous drainage of significantvolumes of �50 mL/24 hrs with orwithout clinical improvement. Con-tinuous drainage may indicate a fistu-lous communication with bowel, bileducts, pancreatic duct, or the urinarytract. Although these communicationsmay be clinically evident, sinographyis still recommended to identify thefistulous tract.

In general, fistulas can be divided intotwo groups: low and high output. Low-output fistulas drain �100 mL/day. Usu-ally, repositioning the drainage catheterto an alternate site adjacent to the leak-ing site is recommended. High-outputfistulas that drain �1000 mL/day have tobe managed with total parenteral nutri-tion and with agents such as cimetidineand somatostatin analogs to reduce fluidproduction from the bowel and pancre-atic duct. Nasoduodenal tubes or otherenteric tubes traversing the bowel defectsmay decrease the quantity of fluid drain-age and hopefully promote healing. Fac-tors that might hinder successful healinginclude the concomitant administrationof corticosteroids, numerous colonic per-forations, underlying bowel pathologysuch as ischemia or a malignancy, immu-nosuppression, or distal obstruction.When such conditions are present, surgi-cal management is often required (7, 8).

Endpoints to Catheter Removal.

1. Catheter output of �10–20 mL perday.

2. Clinical improvement with deferves-cence and decreasing white blood cellcount.

3. Minimal residual cavity on follow-upimaging.

4. Absence of a fistula between the ab-scess and a hollow viscus, such as thebowel or pancreas (8).

Complications of Percutaneous Ab-scess Drainage. Interventional percuta-neous drainage of infected fluid collec-tions is not without risk. Althoughuncommon, described complications sec-ondary to abscess drainage include: septicshock (1–2%), bacteremia requiring sig-nificant new intervention (2–5%), hem-orrhage requiring transfusion (1%), su-perinfection (1%), transgression of bowelrequiring intervention (1%), pleuralcomplication from an abdominal proce-dure (1%), and pleural complication froma thoracic procedure (2–10%) (6).

SPECIFIC INTERVENTIONALPROCEDURES: CHEST

Thoracentesis

Pleural effusions are a common prob-lem in critical care. These may arise in avariety of clinical settings such as cardiacfailure, pneumonia, neoplasia, and trau-matic injury. Light (9) recently reportedthat effusions occur in 20–40% of pa-tients who are hospitalized with pneumo-nia. Nevertheless, although there aremany different pathogeneses for pleuraleffusions, in the critical care setting,pathogenesis is typically due to eitherfluid overload or cardiac and pulmonaryparenchymal diseases. Effusions may alsobe subclassified into complicated and un-complicated effusions. Uncomplicated ef-fusions are simple transudative effusionsthat usually resolve with medical man-agement alone. Examples of complicatedeffusions are empyema, hemothorax, andmalignant effusions. These do not typi-cally respond to antibiotic treatmentalone and require intervention (10).

Thoracentesis is routinely performedand is generally considered safe; however,reports in the literature cite pneumotho-rax, vasovagal reactions, and more infre-quently encountered adverse effects suchas re-expansion pulmonary edema, he-patic or splenic puncture, infections, andhematomas as associated complications(11). Not surprisingly, ultrasound-guidedthoracentesis is associated with a lowerprocedural complication rate. Ultrasoundpermits direct visualization of both thepleural fluid, which appears as an ane-

choic or hypoechoic area, and the sur-rounding structures. It should be notedthat transudative effusions are almost al-ways anechoic, whereas anechoic fluidmay be either transudative or exudative.However, if one identifies septations, de-bris, echogenic material, and thickenedpleura, this almost always indicates acomplex effusion (Fig. 4) (12). Ultrasoundcan also assist in differentiating an effu-sion from atelectasis, consolidation,mass, or an elevated diaphragm. The twomost common indications for thoracen-tesis in the ICU setting are draining ofpleural fluid causing respiratory compro-mise and diagnosing and treating empy-emas. Bedside ultrasound-guided thora-centesis may be safely performed in ICUpatients. Currently, ultrasound-guidedthoracentesis is often reserved for difficultcases, such as mechanically ventilated pa-tients, obese patients, and loculated, atypi-cal or small fluid collections (11).

Technique. If possible, the procedureshould commence with the patient sit-ting with arms elevated and clasped be-hind the head and with the intervention-ist positioned behind the patient. In thecritical care setting, the procedure maybe performed with the patient in lateraldecubitus (the affected side up) or supineposition, if necessary. Initially, oneshould use ultrasound to locate the dia-phragm, liver, and spleen and to gain anappreciation for the overall size of effu-sion. The location of the fluid (or largestfluid pocket) should be marked with apen and sterilized. Some have advocatedinitially using a lower-frequency, 3- to4-MHz sector or vector probe to quickly

Figure 4. Left, ultrasound image of the thoracic pleural cavity reveals a complete anechoic (blackregion identified by the asterisk) fluid collection. No echogenic bright linear septations are seen withinthis collection, and this would be in keeping with a simple pleural effusion. The arrow points to thehemidiaphragm, and the arrowhead points to a solid structure that represents consolidated/atelectaticlung. Right, ultrasound image of the pleural cavity reveals the characteristic appearance of a loculatedpleural effusion under ultrasound, as evidenced by the numerous echogenic linear regions represent-ing thick septations (arrow), with the dark areas representing fluid that would be indicative of acomplex pleural fluid collection, which, in the appropriate clinical setting, could either representadhesions or an infected fluid collection.


survey the thorax and then a 7.5-MHzlinear probe to localize the ribs and vas-cular structures. After ultrasound visual-ization, a puncture site allowing at leastone rib space of fluid above and belowshould be chosen. If the collection is toosmall to allow for this, the patient can beasked to hold his or her breath immedi-ately before aspiration. The area shouldthen be injected with adequate local an-esthesia, penetrating all layers betweenthe skin and pleural surface, after which asmall incision is made with a scalpelblade. The needle should be advanced un-der ultrasound guidance once the site hasbeen marked. Ultrasound should estab-lish the location of the needle within thefluid, which is then further confirmed byaspirating a small amount.

The majority of small pleural fluid col-lections are easily drained with trocarcatheters. Initial aspiration should beperformed with a 19-gauge sheath needlethat also functions as a tandem localizer.A self-retaining 6- to 8-Fr catheter is thentrocared, usually under ultrasound visu-alization. For more substantial effusions,a catheter of �10-Fr may be required, inwhich case, the Seldinger techniqueshould be used. A lateral approach is pre-ferred for placement of a chest tube, withthe catheter situated at the midaxillaryline. The chest tube is then secured to theskin with sutures and attached to a water-sealed drainage system, with suction gen-erally set to �20 cm H2O. There are noclear data and little consensus as to theoptimal time for removal of a chest tube.At our institution, we aim to remove thetube when output has decreased to �10mL/day; however, we recognize that thisis not always the case, and a wide range ofoutput thresholds may be acceptable. Re-peat imaging should be performed to en-sure no undrained collections remain. Af-ter thoracentesis, a chest radiograph toevaluate for pneumothorax should be ob-tained if clinical suspicion exists.

Empyema and Chest TubeInsertion

Empyemas are typically defined aspleural effusions consisting of frank pus,although some have extended the defini-tion to include those with bacteria iden-tified on Gram-negative stain or cultureand with white blood cell counts of�15,000/mL in fluid (13). It should benoted that empyema may arise withoutan associated pneumonic process. No ul-trasound findings are specific for empy-

ema. The diagnosis of a parapneumoniceffusion is based on analysis of the aspi-rated fluid. On ultrasound, the initialstages of an empyema can be character-ized by fluid that appears either anechoicor with fine linear septations. These canoften be drained successfully with a chesttube. Late-stage empyemas are organizedand contain a complex honeycomb pat-tern. Although one could consider drain-age with a larger chest tube, these mayrequire surgical decortication (14). Pa-tients with a parietal pleural thickness of�5 mm, or who have persisting fever andelevated white blood cell counts despitedrainage and appropriate antibiotic man-agement, may also require surgical inter-vention. Drainage can be accomplishedby insertion of a chest tube, placed underultrasound guidance, typically using 8- to14-Fr catheters.

Furthermore, because empyemas arefrequently loculated, successful drainagemay require catheter manipulation thatcan be achieved by changing or up-sizingthe drain or by manipulating and redi-recting the drain under fluoroscopicguidance into a loculated pocket of fluid.Drainage of these loculated empyemas canbe facilitated by instillation of fibrinolyticssuch as streptokinase, 125,000/unit admin-istered every 12 hrs through the tube for upto 48 hrs (15). Reported success rates forchest tube insertion generally range from70% to 94%.

SPECIFIC INTERVENTIONALPROCEDURES: VASCULAR

Central Catheter Placement

Central venous catheterization is cur-rently the most common invasive proce-dure performed in hospitals, and cer-tainly in the ICU. Although centralcatheter placement is an everyday occur-rence in most ICUs, and often performedby junior residents, the procedure is notwithout risk (16). The traditional role ofthe radiologist in the management of pa-tients with central catheters has beenlimited to documenting catheter positionon chest radiographs. There now exists,however, abundant evidence that ultra-sound-guided catheter placement in-creases both the safety and efficiency ofthe procedure when compared with theclassic landmark approach. To put it sim-ply, bedside ultrasound-guided centralcatheter placement is safer for the patient(17). The rationale for ultrasound-guidedcatheter placement is particularly com-

pelling among critical care patients,many of whom present with difficult orcomplicated access.

Venipuncture Site. Venipuncture maybe attempted at the internal jugular, sub-clavian, femoral, or upper-limb veins.Each site is associated with well-docu-mented benefits and disadvantages. Cen-tral catheters inserted with a landmarkapproach typically utilize the subclavianvein. This may be due to the fact that thesubclavian vein has a more predictablepath than the internal jugular vein. How-ever, thrombosis of the subclavian veinmay affect the right upper limb secondaryto impaired venous drainage of the arm.Should such a complication arise, at aminimum, anticoagulation and removalof the catheter may be required. We be-lieve catheterization of the right internaljugular vein with ultrasound guidance ispreferred because, anatomically, it tracesa straight path to the right atrium. In ad-dition, subclavian access increases the risksof pneumothorax and so-called pinch-offsyndrome, in which a central catheter be-comes obstructed due to compression be-tween the clavicle and the first rib (17).

Insertion and Placement. The land-mark approach to venipuncture is accom-plished by passing a needle toward theanticipated line of the vein using super-ficial anatomic landmarks on the skin’ssurface. In contrast, placement of a cath-eter under ultrasound guidance repre-sents a technical improvement. Real-timeultrasound permits the interventionist toassess variant anatomy and patency of thetarget vein and to monitor passage of theneedle throughout the procedure (18). Insome critical care patients, the internaljugular and subclavian veins may not beaccessible. Ultrasound is a particularlyimportant resource in such circum-stances to find alternate routes for access,such as the inferior vena cava, azygos, orintercostals. Catheters placed in thesesites usually terminate in the superiorvena cava or near the right atrium. Withultrasound, there is a significantly re-duced failure rate of cannulation, de-creased need for multiple attempts, morerapid access, and reduced complicationsarising from insertion (18).

Complications. Malpositioned cathe-ters rarely cause complications. However,when complications do arise, they can beespecially devastating, particularly whenthe catheter lodges inside the right atrialwall and causes perforation. Right subcla-vian access is most vulnerable to thiscomplication (17). By employing shorter


(16-cm) catheters, carefully noting cath-eter length and insertion distance, andtailoring the amount of catheter insertedinto the patient’s anatomy, this compli-cation can be reduced to �5%. Even so,correctly positioning catheters under ul-trasound guidance can help reduce thiscomplication, subsequently improvingpatient safety (17).

It is known that complications in-crease if more than two attempts at veni-puncture are unsuccessful. Ultrasoundguidance is effective at eliminating mul-tiple access attempts (16). Failure toplace the catheter and inadvertent vascu-lar puncture are more common than tipmalpositioning, and although rarely asso-ciated with mortality, they still representa significant morbidity issue (17). Real-time ultrasound visualization of the veinduring cannulation should virtually elim-inate these complications. Knowledge ofsafe insertion depths based on a goodunderstanding of the vascular anatomyseen with ultrasound can also minimizeincorrect positioning. We recommendthe use of ultrasound to guide centralvenous catheter insertion, utilizing theinternal jugular vein, and believe that,when possible, ultrasound-guided cathe-ter placement should be the preferredmethod in the critical care setting.

Placement of Inferior VenaCava Filters

Pulmonary embolism is a significantcause of death in critically ill patients(19), and unfortunately, in some cases,even standard prophylactic measuressuch as anticoagulation may be contrain-dicated. Temporary inferior vena cava(IVC) filters are a well-recognized, albeitcontroversial, management tool to pre-vent pulmonary embolism and are typi-cally deployed with percutaneous endo-vascular technique under fluoroscopicguidance. Bedside placement of IVC fil-ters with ultrasound guidance in criti-cally ill patients, however, is becomingmore common in certain institutions.Initially, it is necessary to assess the IVCfor anomalies, thrombus, and acceptablesize and to assess the renal veins for filterdeployment. Filters must be placed im-mediately below the renal veins to beeffective. Although contrast venographyhas traditionally been viewed as the goldstandard, ultrasound has inherent advan-tages such as avoidance of nephrotoxicagents, radiation, and patient transporta-tion. Transabdominal color-flow duplex

ultrasound has been used to evaluate theIVC; it may be limited, however, by poorvisualization in the lower abdomen/upperpelvis (20). Furthermore, anasarca andileus must resolve, often delaying filterplacement. In contrast, intravascular ul-trasound has been reported to be an easyand safe technique used to perform bed-side placement of an IVC filter, with moreaccurate localization of the renal veinsthan contrast venography (21, 22).

Insertion and Placement. The so-called double-puncture technique advo-cated by Ebaugh et al. (2) and Oppat et al.(23) permits real-time ultrasound sur-veillance of IVC filter deployment. Theprocedure is initiated by making two fem-oral venipunctures, approximately 1 cmapart. Two 0.035-inch guidewires arepassed into the superior vena cava underintravascular ultrasound visualization.An 8-Fr sheath is then introduced overone guidewire and a 6-Fr sheath over thesecond. A 10-MHz intravascular ultra-sound probe is then inserted to the levelof the right atrium. After identifying thevasculature, the probe is placed at themost inferior renal vein. If any concernsabout the anatomy or venous anomaliesare raised, then a contrast-enhancedvenogram can be obtained through thefilter delivery sheath. The IVC filter maythen be inserted over the second guide-wire and advanced under ultrasoundguidance until the deployment site isreached. After deployment, the ultra-sound probe filter catheter, guidewires,and sheath are removed. We agree withthe suggestion that any significant sizedifference between the suprarenal and in-frarenal IVC, or large side branches belowthe renal veins, should prompt vena-cavography to better delineate and con-firm normal anatomy (24).

SPECIFIC INTERVENTIONALPROCEDURES: ABDOMEN

The most common use of interven-tional ultrasound in the critical care set-ting for the abdomen is to drain fluid andabscesses. Although percutaneous ab-scess drainage is commonly performedwith CT guidance, ultrasound has manyadvantages particularly relevant to criti-cal care, such as avoiding the need fortransport. However, ultrasound may notbe able to detect abscesses in deep loca-tions that may be obscured by overlyingbowel, vital organs and vessels. Thus, CTremains the imaging modality of choicefor identifying abscesses. However, ultra-sound is well suited for treatment of or-gan-specific, renal, hepatic, and superfi-cially located abscesses and for manyperitoneal abscesses (Fig. 5).

Technique: Intraperitoneal Abdomi-nal Abscess Drainage. The Seldingertechnique is generally preferred, unlessthe abscess is very superficial and large;then, the trocar technique is preferred.With imaging, the fluid collection is lo-cated and an approach selected. Underultrasound guidance, local anesthesiashould be applied using a 19-gaugesheath needle down to the abscess, and asmall amount of fluid should be aspiratedand sent for analysis. Nakamoto andHaaga (25) suggest that if the fluid aspi-rated is purulent, a standard 0.035-inchguidewire should be advanced into theabscess. The tract can then be dilated, asis typical with the Seldinger technique, anda catheter placed. Thin pus does not usuallyrequire catheters of �10 Fr, whereas moreviscous fluid may require 14-Fr catheters.The position of the catheter should be vi-sualized, after which the drainage deviceshould be sutured. Catheters may be at-

Figure 5. Left, complex collection representing an appendiceal abscess. Supportive evidence isidentified by an appendicolith, as identified by the arrow, which is echogenic in appearance, repre-senting calcium. An additional supportive confirmatory ultrasound sign of calcium is the posterioracoustic shadowing that is identified by the arrowhead. Right, color-Doppler ultrasound is also veryuseful in demonstrating increased vascularity to a collection that would be in keeping with theincreased vascularity seen in inflammation. The arrow points to increased vascularity.


tached to Hemovac or Jackson-Pratt drains.The catheter should remain in place untildrainage decreases sufficiently (�10 mL/24hrs) or the patient’s clinical status im-proves (decreased white blood cell count,no fever).

Paracentesis

Ultrasound-guided paracentesis (Fig.6) is commonly performed either as adiagnostic or therapeutic procedure inthe presence of ascites or suspected bac-terial peritonitis. Paracentesis providesalmost immediate symptomatic relief andis usually well tolerated. Initially, ultra-sound scanning of the peritoneal cavity isperformed with a standard-frequency sec-tor or curvilinear probe (e.g., 3.5 or 5MHz) to locate the largest fluid collectionand to allow assessment of the entireabdominal contents. The field of viewmay then be focused with a higher-frequency transducer. This can be accom-plished by using a 7–4 MHz curvilinearprobe with a low-gain setting and opti-mized focal zone (26). Careful attentionshould be paid to any potentially ob-structing vessels such as the epigastricartery. In patients with ascites, one mustbe particularly mindful of possible super-ficial collateral vessels associated withliver disease. Indeed, ultrasound is partic-ularly well suited to paracentesis becauseit can assist in distinguishing transuda-tive from exudative ascites and benignfrom malignant pathogeneses. Transuda-tive ascites usually appear anechoic(completely black) on ultrasound,whereas exudative ascites are often locu-lated fluid collections and may includeparticulates, septa, or fluid interposedwith matted bowel loops (26).

The best areas for paracentesis are 2cm below the umbilical line at the lineaalba or 5 cm superior and medial to the

anterior superior iliac spines. The pre-ferred sites for large-volume paracentesisare the dependent positions, such as theright or left lower quadrants. As men-tioned previously, care should be taken toavoid the inferior epigastric artery, whichnormally travels approximately 4–8 cmlateral to the midline along the lateralthird of the rectus (27). After standardpreparation, local anesthesia is deliveredusing 1% lidocaine down to the parietalperitoneum. A simple needle can be usedfor aspiration and as tandem for eitherthe trocar or Seldinger techniques forcatheter insertion. Nakamoto and Haaga(25) advocate using a 15- or 20-cm-long,19-gauge sheath needle for obese patientsand optional use of the freehand tech-nique, rather than a needle guide, forsmaller collections and for those adjacentto major vessels or the spleen. Complica-tions from paracentesis are infrequent.Injury to the epigastric artery is reportedto occur 0.2–2.0% of the time (27). Hem-orrhage, bowel perforation, and hypoten-sion have also been reported, but theseare rare complications (28).

Subphrenic Abscess

The vast majority of subphrenic ab-scesses are postoperative, often resultingfrom pancreatic, gastric, or biliary surgery.Other common causes include abdominaltrauma, hepatic abscesses, and Crohn dis-ease. Surgical approaches used to treatthese abscesses are associated with highmorbidity and mortality. In contrast, theliterature on percutaneous drainage hasdocumented success rates approaching90%, with a relatively low mortality rate ofapproximately 11%. Thus, percutaneousabscess drainage represents a major ad-vance in management of subphrenic ab-scesses (29–31).

Image guidance is well suited to drain-age of these fluid collections because ul-trasound allows one to differentiate thecollection from adjacent vital structures,such as the liver and diaphragm, and per-mits real-time visualization of the needletip in the abscess, avoiding injury to theadjacent organs. Traditionally, these ab-scesses have been drained using a sub-pleural or extrapleural approach. Ana-tomically, however, these abscesses areoften located in such a way that thepleura, which attaches at the 12th (pos-terior), tenth, (lateral), and eighth (ante-rior) ribs, may obstruct access, making theextrapleural approach technically challeng-ing. It should be noted that Gervais et al.

(32) have advocated an innovative endo-scopic ultrasound-guided drainage ap-proach for these abscesses, with promisingresults.

Either the Seldinger or trocar tech-nique can be used, depending on operatorpreference. Both involve advancing astandard 19-gauge needle sheath underthe ribs into the fluid collection usingreal-time ultrasound guidance. Particularattention should be paid to the trajectoryof the needle and the angle of the cathe-ter. Gervais et al. (32) advocate placingthe needle into the most caudal area ofthe abscess, with the tip pointed in acephalad direction. This permits theguidewire that is inserted through theneedle to move in a cephalad directionunder the diaphragm and, in turn, allowsthe drainage catheter to be inserted im-mediately inferior to the diaphragm, overthe guidewire, accessing the dilated tractand cavity.

Hepatic Abscess

There are three major types of liverabscess. Pyogenic abscesses are by far themost common, accounting for �80% ofcases. In addition, amoebic and fungalabscesses, usually secondary to Entam-oeba histolytica or Candida species, eachaccount for approximately 10% of liverabscesses. Without treatment, hepatic ab-scess is inevitably fatal. Even with timelyantibiotics and drainage, mortality ratesare high, with reports in the literaturevarying between 5% and 25% (33, 34). CTis the diagnostic modality of choice, witha sensitivity of 80–90%; however, ultra-sound has a reported sensitivity of ap-proximately 80% and can identify an ab-scess approximately 1 cm in diameter(35). Many hepatic abscesses at presenta-tion appear loculated and have multipleseptations or portions that appear solid.However, it is worthwhile aspirating orplacing a catheter in all hepatic abscesses,as almost all respond dramatically to per-cutaneous drainage. Intervention is cer-tainly warranted if a patient with pyogenichepatic abscess does not respond to drugtherapy within 48 hrs (Fig. 7).

Percutaneous drainage of hepatic ab-scess is the therapeutic procedure ofchoice and is successfully curative in�90% of cases (36, 37). Access can bemade via an intercostal or subcostal ap-proach, depending on the location of thefluid collection. In general, when at-tempting to drain these abscesses, oneshould be careful to avoid the pleural

Figure 6. Calipers are placed, helping one identifythe depth that has to be traversed percutaneouslyto aspirate the demonstrated intraperitoneal fluidby paracentesis.


space, bowel loops, and large intrahepaticvasculature, visualized using real-timeultrasound guidance. The abscess shouldbe approached from an anterior abdomi-nal route, with the patient lying supine,or via an intercostal approach, with thepatient in lateral decubitus. Some inter-ventionists advocate needle aspirationalone for hepatic abscesses, with excel-lent reported results (37). Clinical man-agement includes monitoring the natureand volume of drainage. Ideally, whiteblood cell counts should normalize within1 wk and patients should defervesce within72 hrs. If drainage persists, or if the natureof the fluid changes, then biliary commu-nication must be suspected and re-imagingand a sinogram are usually recommended.

Renal Abscess

The inherent difficulty in both the diag-nosis and treatment of renal abscesses hasbeen well documented. Salvatierra et al.(38) reported a mortality rate of 56%, andAdachi and Carter reported an approximate40% mortality from perinephric abscesses,even with surgical drainage (39). Prompt

treatment is absolutely essential in themanagement of these patients (38, 40).Common nonspecific clinical signs andsymptoms in patients with renal abscessinclude fever, pain, abdominal discomfort,and leukocytosis. Furthermore, these find-ings are often persistent and have usuallybeen present for a prolonged period of time.In addition, white blood cell counts aretypically only moderately elevated. Elevationof serum creatinine is often not present, but ifelevated, it should always prompt suspicion.

Multidetector CT is the modality ofchoice in diagnosing renal abscesses, whichcan be extremely difficult to visualize underultrasound, particularly in the early stagesand if small. In later stages, however, theymay be well seen (Fig. 8). Once identifiedunder multidetector CT, these are best as-pirated and drained using ultrasound in theICU setting. Very small abscesses (�3 cm)have been treated successfully in the pastwith antibiotics alone. However, aspirationcan help speed resolution. Either CT orultrasound image–guided percutaneousdrainage of these abscesses is often the bestchoice, with reports of minimal morbidityand reasonable results (41, 42). Whendraining renal abscesses using percutane-ous intervention, the best route for needleentry is through an oblique posterolateralapproach along the Brödel line, locatednear the posterior axillary line, approxi-mately 3 cm below the 12th rib. This ap-proach avoids most of the erector spinalmuscles, pleural space, and bowel.

Pancreatic Fluid Collections

Pancreatic abscess can be safely man-aged with percutaneous drainage, butonly if there is no solid necrotic debris of�1 cm in diameter. Patients with exten-sive necrosis should not be treated withpercutaneous therapy and, instead, re-

quire surgical debridement. Thus, it isimportant to conduct preproceduralscreening to rule out this contraindication.The gold standard for imaging pancreaticabscesses is still enhanced multidetectorCT. However, magnetic resonance imagingis also proving to be a valuable imagingmodality, with reported high sensitivity andspecificity rates. Therefore, the role of real-time ultrasound-guided drainage of pancre-atic collections is essentially limited to anICU setting, but only after predrainage,guided by multidetector CT/magnetic reso-nance imaging (Fig. 9). As stated previ-ously, it is essential to avoid potentiallyinfectious complications from unrecog-nized necrotic debris that cannot be re-moved with drainage and requires surgicalintervention (43). The most common mo-dality used to guide drainage catheterplacement is CT, with success rates re-ported to be approximately 86%. Note thatduring the procedure, care should be madeto avoid the colon.

Pseudocysts of �6 cm that have beenpresent for �6 wks usually require treat-ment. Drainage can be percutaneous, sur-gical, or endoscopic. The Seldinger ap-proach is most commonly utilized fordrainage of pancreatic abscesses, with useof a 0.035-inch guidewire and 19-gaugetrocar needle. Catheter size should be se-lected based on viscosity and quality of theinitially aspirated fluid, and the cavityshould be irrigated with saline until all pu-rulent fluid and debris have been removed(44). Catheters are removed according tothe standard criteria outlined previously,but it should be noted that pancreatic ab-scesses often required prolonged drainage,with a mean of 32 days (45). An alternatetreatment option involves an invasive proce-dure that utilizes endoscopic ultrasound-guided creation of a transgastric or duodenalfistula allowing for drainage. Subsequently,the fistula can be sealed with glue once treat-ment is completed.

Figure 7. Left, solid collection, identified by the arrow, in keeping with a subphrenic perihepaticabscess. The arrowhead identifies the echogenic right hemidiaphragm and the star identifies the liver.Right, ultrasound image of the left lobe of the liver reveals a cystic structure (arrow) with internallinear bright areas that either represent septations, internal debris, or infected material that, in theappropriate clinical context, would be in keeping with a liver abscess.

Figure 8. Arrow points to a complex collectionthat would be indicative of an abscess within theupper pole and interpolar region of the rightkidney.

Figure 9. Ultrasound image of the pancreatic bedreveals a solid collection demarcated by the cal-ipers. The echogenic structure identified at cen-ter in the collection is the catheter (arrow).


Acute Cholecystitis(Percutaneous Cholecystostomy)

Clinically, both forms of cholecystitis,calculus and acalculus, are indistinguish-able, and initial treatment is the same(i.e., decompression of the gallbladder).However, patients with calculus chole-cystitis will often require subsequentcholecystectomy. In this cohort, ultra-sound is the imaging modality of choice.Ultrasound findings of acute cholecystitis

include 1) a distended gallbladder of �5cm, 2) gallbladder wall of �3 mm inthickness, 3) positive Murphy sign (trans-ducer-elicited tenderness over the gall-bladder), 4) gallstones/sludge, and 5)pericholecystic fluid (46). In acalculuscholecystitis, similar findings are ob-served, except, of course, the presence ofvisualized calculi. However, echogenicsludge may still be present in a distendedgallbladder, and a thickened wall andpericholecystic fluid may indicate thepresence of gangrene (46). Other findingsthat might suggest gangrenous cholecys-titis are asymmetrical wall thickeningand intraluminal debris (Fig. 10).

In the appropriate clinical setting, thepreviously described imaging findings al-low for the diagnosis of acute cholecysti-tis in 94% of patients. However, it isimportant to remember that gallbladderwall thickening may also occur in otherdiseases, such as acquired immunodefi-ciency disease, and hepatitis. Further-more, ultrasound has several pitfalls:first, calculi are often found incidentallyin critically ill individuals without gall-bladder disease; second, a Murphy signmay be difficult to elicit in some severelyill patients who may be comatose or non-responsive to painful stimuli (8).

An alternate imaging modality thathas a reported sensitivity and specificityof up to 96% for the diagnosis of acutecholecystitis is a nuclear medicine hepa-toiminodiacetic acid (HIDA) scan. It isbased on the principle that the radiophar-maceuticals introduced intravenously areprimarily excreted by the hepatobiliarysystem. If no radiotracer material is iden-tified within the gallbladder up to 4 hrsafter introduction but instead is visualizedwithin the bowel, common hepatic, orcommon bile duct, it implies the diagnosisof acute cholecystitis due to a cystic ductobstruction. This imaging test can be ex-

tremely useful in confirming the diagnosisof acute cholecystitis.

Treatment. Initial treatment is de-compression of the gallbladder. This canbe accomplished by either placement of adrainage catheter or by simply aspiratingthe gallbladder with an 18-gauge needle(Fig. 11) (47). The latter method is moreuseful in diagnosing and treating patientssuspected of having acalculus cholecysti-tis (47). Relief of symptoms after gallblad-der aspiration is not only diagnostic butcan also be significantly therapeutic.Thus, simple gallbladder aspiration is anexcellent method to treat acalculus cho-lecystitis in many patients (8).

The gallbladder can be drainedthrough either a transhepatic or directtransperitoneal approach. In acute chole-cystitis, the gallbladder is usually ex-tremely distended and often extends be-low the liver margin, making it easilyaccessible to direct puncture. Either theSeldinger technique or a one-step trocartechnique can be utilized (8). The advan-tages for a transhepatic approach include1) lower risk of colonic perforation, 2)lower risk of loss of access to the gallblad-der, and 3) lower risk of bile leakage intothe peritoneal cavity. The tract createdthrough the liver is usually peripheraland color Doppler can be used to identifylarge vasculature that must be avoided. Ifone attempts the transhepatic approach,the coagulation profile of the patientneeds to be optimized. Most commonly,this procedure is performed under ultra-sound guidance in the critical care pa-tient. The indications for a direct trans-peritoneal approach include a gallbladderthat is relatively accessible with a one-stick trocar technique. However, thetranshepatic approach can also be uti-lized in this setting and is often the pre-ferred approach of most interventionalradiologists. The advantages of a transhe-patic approach have been outlined previ-ously, and in this case, the Seldingertechnique should be utilized for catheterplacement.

Under ultrasound guidance, the initialpuncture is performed with an 18-gaugeneedle, and 5 mL of bile is usually re-moved to partially decompress the gall-bladder and provide a sample for Gram-negative stain and culture. The positionof the needle tip should be visualizedunder ultrasound and its location withinthe gallbladder confirmed. The needlecan then be used as a tandem for eitherthe one-stick direct trocar technique or,alternatively, a guidewire can be inserted

Figure 10. Top, ultrasound imaging of the rightupper quadrant reveals a distended, thick-walledgallbladder (star) with numerous gall stones (ar-rowhead). Extensive posterior acoustic shadow-ing is demonstrated by the fan-shaped region ofdecreased echogenicity (arrow), which is a char-acteristic ultrasound finding of a calcified struc-ture. Calcified substances do not allow transmis-sion of the ultrasound beam, therefore giving theappearance of decreased echogenicity. Middle,color-Doppler image of the gallbladder that isuseful in demonstrating increased vascularityidentified by the arrow (tubular structures rep-resenting vessels). This appearance is highly sug-gestive of an inflamed gallbladder. Bottom, echo-genic material layering posteriorly within thegallbladder (arrow) represents a significant de-gree of sludge. In the appropriate clinical con-text, this would be in keeping with acalculuscholecystitis.

Figure 11. Aspiration of a thick-walled gallblad-der. The linear echogenic structure (arrow)within the gallbladder is the aspiration needle.


through the needle, after which the tractis dilated and a pigtail-shaped drainagecatheter (nephrostomy tube) is insertedover the shift-shaft J-guidewire. Thecatheter is then left to drain via gravity.Rapid evacuation should be avoided be-cause it may trigger a vasovagal reaction.After percutaneous decompression, dra-matic clinical improvement in symptomscan be seen in about 90% of the patients(48). Failure of clinical improvementwithin 24–48 hrs is suspicious for analternate pathogenesis or the presence ofcomplications (bile peritonitis, bile ductobstruction) (Fig. 12). Gangrene of thegallbladder should also be suspected ifthere is persistence of symptoms afterdecompression.

Catheter Removal. Usually, the drain-age catheter can be removed after thetract has matured and patency of the cys-tic duct has been demonstrated. Becausethe time frame for tract maturation isapproximately 3 wks, catheters can beremoved safely after �3 wks. A cholecys-togram should also be obtained to assesspatency of the cystic duct and to identifycalculi that may have been missed oninitial imaging.

Percutaneous Nephrostomy

Percutaneous nephrostomy was firstdescribed in 1955 and is now a commonprocedure used to relieve urinary tractobstruction (Fig. 13) in the presence ofan increased white blood cell count, fe-ver, pyohydronephrosis, and a rapidly in-creasing creatinine level. Ultrasoundguidance is an excellent method becauseit again permits real-time visualization ofneedle placement necessary for obtaininginitial access to the renal collecting sys-tem. This is particularly true if the pa-tient has mild hydronephrosis. Antibioticprophylaxis for patients with suspectedpyonephrosis or renal stone disease, or

both, should always be used before anyintervention. In ultrasound-guided per-cutaneous nephrostomy, one generallytargets a posterior calyx using an obliqueposterolateral approach along the Brödelline, near the posterior axillary line, ap-proximately 3 cm below the 12th rib. Thisis preferred because it avoids the pleura,erector spinal muscles, colon, liver, andspleen and has the lowest risk of arterialinjury and subsequent hemorrhage (8). Itshould be noted that this only applies tonative kidneys; for transplant kidneys,one should consider targeting the ante-rior calyx because of the superficial loca-tion and different axis. Initial trajectory ismade with a 20-gauge Chiba or 18-gaugesheath needle. After the position is con-firmed and is satisfactory, the tract can bedilated using the Seldinger technique,and an 8- or 14-Fr catheter, self-retainingnephrostomy tube attached to a closed-system drainage bag can be placed (49).

Complications include significantbleeding requiring transfusion, bactere-mia, and inadvertent puncture of thepleura or abdominal viscera (e.g., liver,colon, and spleen). In addition, catheterdislodgement is a common problem, andas such, catheters should be securely su-tured in place. Retroperitoneal urine ex-travasation, or significant macroscopichematuria causing clot colic and/or cath-eter blockage, may require further inter-ventions (50).

SPECIFIC INTERVENTIONALPROCEDURES: PELVIS

Pelvic abscesses most frequently ariseas a complication of gastrointestinal dis-orders typically related to acute appendi-citis, bowel diverticulitis, and Crohn dis-ease. Postoperative fluid collections are

also common, particularly after bowelsurgery, as are gynecologic pathogeneses,the most prevalent being tubo-ovarianabscess arising secondary to pelvic in-flammatory disease (8). Approaches forpercutaneous drainage of pelvic abscessesinclude transabdominal, transgluteal,transvaginal, and transrectal routes (7).Infected collections present within thepelvis pose unique technical challengesdue to deep location, surrounding bonypelvis, overlying bowel, genitourinarytract, and overlying vascular structures.If a safe anterior approach exists, it is thepreferred route for percutaneous evacua-tion, especially when utilizing the trocartechnique. However, due to gravity de-pendence of the fluid, the majority of theinfected fluid collections occur posteri-orly in the pelvis, and drainage of thesecollections may require alternative entrysites such as transgluteal, transrectal,and transvaginal (7, 8).

Transgluteal Drainage. This is techni-cally challenging, and transgluteal drain-age of abscesses is usually performed un-der CT guidance. The best access route isinferomedial, staying as close as possibleto the sacrum to avoid injury to the sci-atic nerve and internal iliac arterialbranches. Persistent catheter-relatedpain may be due to the close proximity ofthe tract and the sacral plexus. Thisshould be re-evaluated and the catheterrepositioned under CT guidance. Compli-cations include pelvic hematoma andcatheter kinking when the patient lies inthe supine position. This can be mini-mized by encouraging the patient to lie inthe decubitus position if possible.

Transrectal and Transvaginal Drain-age. Experience with these routes ofdrainage is growing, and these tech-niques seem to be effective and well tol-erated. Needle guides are available forboth transrectal and endovaginal probesthat help guide the needle into the fluidcollection. Success rates in the range ofapproximately 88% have been reported inthe literature in the treatment of pelvicabscesses by ultrasound-guided transrec-tal aspiration using 18-gauge needles(51). After aspiration, the infected cavitieswere also lavaged with saline. Althoughno permanent catheters were placed, thereported results were comparable withthose reported for catheter drainage.Thus, it seems that immediate catheterdrainage is not necessarily indicated andthat most of these patients may experi-ence similar benefit with one-step aspira-tion lavage and antibiotic therapy.

Figure 12. Demonstrates clinical utility of ultra-sound in detecting biliary dilations, seen here asnumerous tubular cystic structures (arrow)within the liver.

Figure 13. Ultrasound image of the right kidneyreveals connecting, dilated, urine-filled tubularstructures (arrow), representing a dilated renalcollecting system in keeping with hydronephro-sis. In this setting, the patient had an increasedwhite blood cell count and a fever, necessitatingpercutaneous drainage.


However, enteric abscesses that havecommunications with the gastrointesti-nal tract pose a unique problem. In thesecases, it is important to recognize that acommunication with the bowel lumenexists, and if this communication is notallowed to close before removal of thecatheter, successful drainage will not beaccomplished.

Some Pearls and Pitfalls to Be Re-membered. Usually, transrectal guidanceand abscess drainage is better toleratedthan transvaginal, as the transvaginal ap-proach is associated with a greateramount of pain. As such, it is generallyagreed on that the transrectal approach ispreferred. Furthermore, it seems that al-though the transrectal route is better tol-erated utilizing the Seldinger technique,the transvaginal route is better toleratedusing the trocar-type technique (8).

MISCELLANEOUS

In addition to the procedures outlinedabove, ultrasound is providing new andever-increasing interventional roles atthe bedside of the critical care patient.For example, percutaneous dilational tra-cheotomy, used to establish tracheosto-mies for mechanically ventilated patients,can be performed with reduced compli-cations, particularly bleeding from neckvasculature (52). Chen et al. (53) havereported promising results with ultra-sound-guided inguinal hernia reduction,a common abdominal emergency. In ad-dition, ultrasound can facilitate suprapu-bic cystostomy, an emergent decompres-sive procedure for urinary retention, byguiding needle aspiration of the bladderwith significantly increased success rates(54). Lumbar puncture, a common pro-cedure in the ICU, can be facilitated byuse of a 7.5-MHz linear probe placed in thetransverse plane over the midline of the backat the level of the iliac crests; in this view, thespinous processes are visualized as distinctechogenic bright shadows (55). There areeven reports of ultrasound being success-fully employed to facilitate spinal nerveroot blocks.

Ultrasound technology continues todevelop as well. Color-flow mapping rep-resents an advanced form of color-Doppler imaging. In this modality, meanvelocity and flow direction are colorcoded, the information is then superim-posed on a conventional real-time ultra-sound image, and the nonmoving imagesare subtracted by a process called autocorrelation. Perhaps the most significant

advances are related to the developmentof three-dimensional ultrasound with theuse of multiplanar reformatted imagesdisplaying three orthogonal planar B-mode images simultaneously. This volu-metric display capability will undoubtedlyprove superior to conventional two-dimensional display because it permitsvisualization from three complementaryviews, allows visualization of the targetfrom any orientation, and provides theability to scroll through complex struc-tures (56).

CONCLUSION

Ultrasound has markedly progressedboth in its portability and breadth of ap-plication during the past decade. Withcontinuing advances such as those out-lined above, it can be anticipated that therole of ultrasound will continue to ex-pand in the ICU. Ultrasound affords theinterventional radiologist a unique tooldue to its affordability, portability, lack ofradiation or nephrotoxic contrast expo-sure, and the ability for real-time visual-ization. Indeed, ultrasound in the criticalcare setting is now truly indispensable forfacilitating rapid diagnosis and allowingfor more convenient and less complicatedtherapeutic procedures. Minimally inva-sive procedures are particularly desirablein the ICU, and the significant benefit ofperforming procedures at the bedsidewithout delay or patient transportationrisk should not be underestimated.

It is therefore important that inter-ventionists take the initiative and utilizeultrasound, particularly with respect toprocedures such as central catheterplacement, for which there is already asubstantial amount of evidence demon-strating benefit. Similarly, intervention-ists should be encouraged to continue toexpand the applications of this uniquetechnology in the critical care setting.Nevertheless, although it is likely thatbedside ultrasound-guided interventionswill increasingly become the norm ratherthan the exception in the ICU, like somany other operator-dependent tools, ac-curacy and effectiveness depend on thefamiliarity and skill of the operator. Thus,further refinement of training, creden-tialing, and standards will need to be ad-dressed. In the future, with advances inultrasound technology and as more oper-ators become familiar and adept with itsuses, the interventional applicability anddiagnostic potential of ultrasound as an

imaging modality will most certainlycontinue to improve.

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